In plastic pipe systems, connections between the various components must be sealed to prevent escape of fluids from the connections. The connections typically comprise an enlarged bell which receives a spigot. The spigot and bell can be formed as segments of pipe lengths or connecting members, such as elbows, T's, etc. In this application, the terms "fitting" and "pipe" are intended to include both pipe lengths and connecting members.
The seal between the bell and spigot is conventionally provided by a gasket mounted in one of the components of a connection and sealingly and resiliently engaging the other component. Most often, the seal is mounted in the bell and has at least one radially inwardly projecting sealing lip which is engaged and deformed by the spigot such that a tight interference fit is formed between the spigot and sealing lip to prevent the escape of fluid.
Gaskets formed exclusively of elastomeric material, such as natural rubber, are disadvantageous since they can be displaced from their intended position so as not to provide an adequate seal. For example, such gaskets may blow out of their mounting when pressurized or may be pushed from their intended position during insertion of the spigot within the bell.
Gaskets reinforced with metal bands can be deformed and the metal can corrode rendering the gaskets useless. Moreover, when such gaskets are made an integral segment of the pipe spigot, deformation or corrosion of the metal band renders the entire pipe section useless.
More recently, gaskets reinforced with plastic locking rings have been increasingly used. Such gaskets are described in U.S. Pat. No. 4,343,480 to E. D. Vassallo. However, the cost of elastomeric materials, such as rubber, has significantly increased in recent years, thus forming a significant factor in the cost of fittings. Although the gaskets utilizing plastic locking rings contain less rubber than those made entirely of rubber, the rubber still forms a major portion of the gasket and thus greatly affects its cost.